Polyalkylbenzene carboxylic acid and process of preparing it



Patented Apr. 14, 1953 PQLY'AIZKYLBENZENE CARBOXYIJI'C ACID AND PROCESS OF PREPARING" IT Maurice. J, Schl ter, El Cerrito, tGaJit, assignor. to California Research cqlpmlatiiqh 516111 .Fran: cisco CaliL, acorl oration of Delaware NoDrawing. Application June-19.11951, .Serial No. 2 312,455

The-present" inventlon is concerned with the able as intermediates in the production of various-.simportant chemicals such as modified alkyd resins, ipolyme-rizable vinyl esters, modifiers for unsaturated" polyesters, specialty greases, plasticizers', surface-active agents, dyes, pharmacenticalmandsperfumery mtermediates- .Eorlthe pr duct n o mo ifie 3 33 91 3. 7 15 b n e boxylic L acids having high melting points inaddition to; chemical stability are 7 particularly desirthi s n e t em ms obtainedr rom h ive a harderandslossier final. product characterized by'grea'ter durability under normal usage.

Euro benzene .carlooxylic acids. having :alkyl groups of predetermined structure in specific isomeric-arrangement on the benzene nucleus which "would be useful in present-day applications have heretofore been very diflicultto obtairicingood yields. Alkylation of benzoic acid or. its, homologues with a. specific alkylating agent has, proved impractical because otthe inherent resistance of'benzene carboxylic acids to the; direct introduction ofnuclear alkyl groups. It has now been found that essentiallypure 3,5, di-tertiary-butylbenzoic, acid, a novel benzene carboxy ic acid distineuishedbyits c mi al res es t leanattack and; unusually hi h: meltin p can benrenared inexcellsntdiel-sis;

by; alkylating... toluene, .ethylbenzene or 7 other slniilarshort-chainalkyl benzene with a tertiary- Bhtriilting} agent and oxidizing the 3,5-di-tertiaryj butyltoluene', 3,5-di-tertiary-butylethylben- Zens or other 3,5-di-tertiary-butylalkylbenzene thus obtained. This is a surprising discovery since; in general, "polyalkylbenzens containing yl roup 10f more than, o fierbsnewm not be oxidized cleanlyto .give'a single-product.

-The--3,5 di-tertiary-butylbenzoie acid of this invention .is unique because, due to'the steric hindrance of the bulls-y-symmetrically-arranged tertiary-butyl groups, all the ring positions are essentially blocked. It thus resists further substitution and chemical attack on the benzene nucleus. This chemical stability derived from its unusual molecular structure makes the 3,5-ditertiary-butylbenzoic acid particularly useful .as an intermediate in chemical reactions where it is desirable to avoidthe formation of by-products. For example, vinyl esters of aromaticacidsgen-l erally form insoluble, infusible polymers because of" cross-linking through thearomatic nuclei.

is not possible with the ac-m mmary accordingly, allows preparation of, valua leesolr- .ubleand fusible vinyl ester polymers; Thanhusu lly high mel nspointof the, 3.5-di .ertiary butylbenzoic acid which is: much higher than that of any other-knownalkyl-benzenecarboxylie acid of equivalent molecular weightyalso makes it very desirable for theproduction ofmodified alkyd resins where hardness, depth of gloss-and. durability of the final product are important:

factors.

The process of preparing3,5-dietertiarybutylbenzoic acid, according to the present invention, is easily carried out. Materials which are commonly available are used as reactants. When the reactants are properly combined pursuant to the method of this invention, more particularly described hereinafter, the reaction proceeds in a surprisingly straight-forward manner to produce the 3,5 di-tertiary-.butylbenzoic acid in goodyield'.

In preparing the 3,5-di-tertiary-=butyltolueneand 3,5-di-tertiary-butylethylbenzene hydrocarbon intermediates, according to this invention, either toluene, ethylbenzene or a short-chain alkyl benzene havingat least one hydrogen atom on the carbon of the alkyl group adjacent to the benzene nucleus may be employed as starting material. Toluene is preferred since the methyl group is oxidized directly to the desired carboxyl group of the final product with lower'consumption of the oxidant. Furthermore, ethylbenzene has; a tendency to form a variety of side reaction products not obtained when toluene is tertiary- &5. or. ethylhenz nediiters withdifierentzasentsxmr butylated.

Any tertiary-butylating agent may be employed to produce the dl-tertiary-butyl substituted toluene and ethylbenzene. Suitable alkylating 'materials include isobutene, tertiarybutyl-chloride, tertiary-butyl alcohol, tertiary butyl mercaptan and di-isobutylene. Tertiarybutyl chloride and isobutene arepreferred, particularly the latter, becauseof their ready availahuny.

From about 1 to about ,3. moleso j tertiarybutylating agent per mole of toluene or ethyl? benzene are employed in thealkylation reaction. Either smaller or larger proportions may be used under certain conditions but ordinarily the molar ratio of tertiary-butylating agent to toluene or ethylbenzene should not be greater than 5 in order toavoid butene polymerization andthe formation of undesirable complexes. mole ratio of tertiarydoutylating:agent to toluene The op imum.

example, a large excess of tertiary-butyl chloride may generally be employed, because the unreacted tertiary-butyl chloride is not altered and may be recovered and recycled. Isobutene, on the other hand, is polymerized and involved in other side reactions which decrease the yield of the desired product and for this reason is best used in a ratio of 1-2 moles per mole of monoalkylbenzene. In such cases good ultimate yields are obtained by recycle of the mono-tertiarybutylalkylbenzene obtained in the reaction. For present pur oses. it has been found that about 1.5 to 2 moles of tertiary-butylating agent per mole of toluene or ethylbenzene is most satisfactorv.

The alkvlation reaction is desirably carried out in the presence of a catalyst of the type of hydro en fluoride, aluminum chloride. boron trifiuoride, aluminum bromide. ferric chloride, phosphoric acid, etc. Temperature in the range of from about 20 C. to about 125 C. may be emploved. When the reaction is carried out in. the presence of an hydrogen fluoride catalyst. as presently preferred. temperatu es in the ran e of from about C. to about 50 C. are particularly satisfactory. Althou h atmospheric, superatmospheric or subatmosnheric pressures may be emploved durin the alkylation, pressures above atmospheric in the range of from about 30 to about 50 pounds per square inch gau e are more desirable when an hydrogen fluoride catalyst is used in rder to avoid vaporization of the catalyst.

The 3.5-di-tertiary-butyltoluene and 3,5 -ditertia -o1itvlethvlbenzene may he recovered from the alkylate reaction mixture bv methods such as fractional distillation, crystallization, solvent extraction, etc. For present purposes. a com-bination fractional disti ation and crystalli ation has been found most satisfactory. In this latter type of separation, it is possible to obtain essentially pure 3.5-di-tertiary-butyltoluene because of the characteristic high melting point of this material. 3,5-di-tertiary-butylethylbenzene does not crystallize readilv. but this material can he conveniently obtained by fractional distillation in a purity suitable for oxidation.

The 3,5di-tertiary-butyltoluene and 3,5-di tertiary-butylethylbenzene may be oxidized to 3,5-di-tertiary-butylbenzoic acid by the use of various alkaline and weakly acid oxidizing agents. Strongly acid oxidizing agents such as mixtures of chromic acid and sulfuric acid are preferably avoided to prevent acid catalyzed de-alkylation reactions. oxidizing agents such as alkaline permanganate, sulfur and aqueous alkali mixtures, dilute nitric acids, etc. may be employed. Oxidation with air or oxygen in the presence of catalysts such as cobalt and copper Soligens, manganese oxide, vanadium oxide, tin vanadate, etc. may be used.

When the oxidation is carried out by means of alkaline permanganate or dilute nitric acid, the 3,5-di-tertiary-toluene or 3,5-di-tertiary-butylethylbenzene is mixed in the vessel with the oxidizing agent and heated, usually at a temperature within the range of from about 80 C. to about 100 C. In oxidizing the 3,5-di-tertiary-butyltclnone and the 3,5-di-tertiary-butylethylbenzene with oxygen or air in the presence of oxidation catalysts, a liquid phase process operating at from about 110 to 150 C. is preferred. However, vapor phase cxidations may be successfully carried out at temperatures generally not exceeding about 600 C.

The 3,5-di-tertiary-butylbenzoic acid may be separated from the reaction mixture produced in Example I .Preparation of 3,5-ditertiary-butyZ- toluene by allcylation of toluene with isobulene 1104 parts of toluene were placed in a flask equipped with a mechanical stirrer, gas addition tube, and vent tube. The flask Was then immersed in an ice bath and 354 parts of liquid hydrogen fluoride were added. Over a period of 6 hours 898 parts of isobutene were introduced. The reaction mixture was cooled and neutralized with potassium hydroxide. The hydrocarbon phase and ether extract of the aqueous phase were dried over calcium chloride and distilled. The final product had the following analysis:

Percent Yield by Parts by Weight Weight Based on Toluene Charged Toluene Mono-tertiary-butyltoluene 1, 041. 5 58. 5 3,d-(li-tertiary-butyltoluene.. 630. 0 25. 7 High-boiling products 137. 7

The 3,5di-tertiary-b utyltoluene when re-crys-v tallized from ethanol melted at 31.0-31.9 C. It had a boiling point of 234-237" C. at 760 mm. Hg.

Example II.Prepamtion 0 3,5-di-tertz'ary-butyltoluene by alkylation of mixed tertiary-butyltoluenes with tertiary-butyl chloride A mixture of about 357 parts of meta-tertiarybutyltoluene and 357 parts of para-tertiary-butyltoluene'was cooled to 0 C. in a copper flask immersed in an ice bath. About 198 parts of liquid hydrogen fluoride were then added. The mixture was agitated vigorously and about 275 parts of tertiary-butyl chloride were added over a period of one hour. After stirring for about 3 hours, the product was distilled. The crude product had the following analysis:

Percent Yield by Weight Parts by Based on Weight Unrecovered Tertiarybutyltoluenes Toluene Mono-tertiary-butyltoluenes 3,5-d1-tcrtiary-butyltoluene A sample of re-crystallized 3,5-di-tertiary-butyltoluene was found to have a melting point of 31.4 C.

Example III.-Al7cylat2'on of toluene with tertiarybutyl chloride in the presence of aluminum chloride catalyst Approximately 200 parts of anhydrous aluminum chloride were placed in a flask equipped with stirrer, reflux condenser, thermometer and addition funnel. 276 parts of toluene were added and the mixture stirred for about 30 minutes to dissolve a large portion of the aluminum chloride. 588 parts of tertiary-butyl chloride were added Percent Yield by Weight Based on Toluene Charged Parts by Weight Tertiary-butyltoluenes Di-tertiary-butyltoluenes Viscous oil (polybutenes, etc.

Example IV.Preparatzon of 3,5-di-tertz'arybatylethylbenzene Isobutene (approximately 2.5 parts per minute) was passed into a vigorously stirred mixture of 1274 parts of ethylbenzene and 333 parts of liquid hydrogen fluoride contained in a copper flask immersed in an ice bath. After six hours, gas addition was stopped and stirring continued for thirty minutes. The reaction mixture was poured on crushed ice, neutralized with excess potassium hydroxide, separated, dried and distilled through a 30 plate column. Mono-tertiary-butylethylbenzenes (B. P. 204-212 C. at 760 mm.) were obtained in 41% yield based on ethylbenzene charged, 3,5-di-tertiary-butylethylbenzene (B. P. 128-131 C. at 20 mm. pressure) was obtained in 20% yield. A center cut product had the following physical properties: B. P. l30.0 C. at 20 mm.; n 1.4890; c14 0.8575. The 3,5-di-tertiarybutylethylbenzene structure was confirmed by comparison of the infrared and ultraviolet spectra with those of other 1,3,5-trialkylbenzenes.

Example V.Prepamtion of 3,5 -dz'-tertiary-batylbenzoic acid 344 parts of 3,5-di-tertiary-butyltoluene, 1200 parts of pyridine, 600 parts of water and 142 parts of potassium hydroxide were mixed in a threeneck flask equipped with mechanical stirrer, reflux condenser, thermometer, and addition funnel and heated to a temperature of about 95 C. 666 parts of potassium permanganate were added over over a 3-hour period to the mixture with vigorous stirring while maintaining the temperature at about 95 C. After the addition was complete, stirring was continued for another 1 /2 hours at 95 C. The manganese dioxide formed product gave about 80 parts of unreacted 3 .5-ditertiary-butylbenzene.

The aqueous phase obtained in the above process was concentrated on a steam plate and the crude acid precipitated by acidifying with hydrochloric acid. Additional crude acid entrained in the manganese dioxide precipitate was recovered by suspending th manganese dioxide precipitate in dilute hydrochloric acid and adding sodium bisulfite until the dark-brown particles were all dissolved. A white solid remaining in suspension was collected on a filter, washed with water, redissolved in potassium hydroxide, reprecipitatecl with acid. filtered, washed with water and dried. The combined portions of crude acid were recrystallized from benzene and 197 parts of 3,5-ditertiary-butylbenzoic acid were obtained. The yield amounted to about per cent of theoretical based on umecovered hydrocarbon.

The 3,5-di-tertiary-butylbenzoic acid obtained by the above experiment was in the form of colorless needles characterized by the following inspections:

Melting point, l72'.6-173.0 C. Neutral equivalent, 236 compared to calculated of 234.3. Carbon and hydrogen analysis:

C=77.14%; 77.27% H: 9.53%; 9.51% Theoretical References Cited in the file of this patent UNITED STATES PATENTS Name Date Hearne et al Dec. 18, 1951 Number 

